Power inverters (or in short inverters) are electronic devices which transform direct current (DC) to alternating current (AC). In particular, inverters play nowadays an economic and environmental role which is more and more important in the frame of transformation of DC current produced by solar panels, batteries or similar sources into AC current for domestic or industrial use as well as in electric cars.
Inverters manufactured by the Applicant for commercial and industrial companies permit saving of their critical applications by using energy stored in batteries, during distribution grid breakdown. Inverter Media™ manufactured by the Applicant already allows to reach a power density of 680 W/liter at 2 kVA.
Inverters used for example in electricity production facilities from solar energy still have a noticeable size (typically 50 liters or the size of a portable cooler). Size reduction of >10× in volume, i.e. typically shrinking down to something smaller than a small laptop would enable powering more homes with solar energy, as well as improving distribution efficiency and distances ranges reached with electrical grids. Future will thus be dedicated to more robust, more reliable and more intelligent power inverters.
In order to achieve very high power density and consequently smaller conversion systems, designers of inverter topologies had primarily to target increased efficiency and common mode (CM) noise reduction. Higher efficiency has been achieved thanks to improvements in semiconductor materials and processing, as well as in magnetic materials. Use of wideband-gap semiconductors (silicon carbide—SiC or gallium nitride—GaN) allows to improve efficiency in high frequency power converters, while the latter allow increasing switching frequency and thus reducing passive components size.
It is known that EMI noise is both in the form of conducted EMI, i.e. noise travelling along wires or conducting paths and through electronic components and in the form of radiated EMI (RFI), i.e. noise travelling through the air in the form of electro-magnetic fields or radio waves. In high-speed switching converters (frequency typically from 50 kHz to 1 MHz), most of the conducted EMI comes from the switching transistors and from the rectifiers. For preventing such EMI noise, one generally uses EMI filters made of passive components such as capacitors and inductors forming LC circuits. Conducted EMI is divided into common-mode noise (CMN) and differential-mode noise (DMN). CMN flows in the same direction in line and neutral AC power conductors, is in phase with itself relative to ground and returns to ground. Suitable CMN filter comprises inductors L100, L200 placed in series with each power line and respective Y-capacitors C100, C200 connecting each power conductors to ground (see for example CMN filter 100 in FIG. 1 in the case of a DC/AC converter). DMN exists between AC line and neutral conductors and is 180° out of phase with itself. Suitable DMN filter comprises C340 X-capacitors bridging the power lines, possibly supplemented by differential-suppression inductors L300, L400 (see for example DMN filter 101 in FIG. 1 in the case of a DC/AC converter).